1. Field of the Invention
The present invention relates to an etching apparatus for a liquid crystal display device and more particularly to an etching apparatus for uniformly etching a glass substrate.
2. Discussion of the Related Art
Significant research is being conducted on various flat display devices, for example, on liquid crystal display (LCD) devices, plasma display panels (PDP), electroluminescent displays (ELD), and vacuum fluorescent displays (VFD). The LCD device is one of the most commonly used flat display devices and active research is being pursued in this area.
The LCD device includes a liquid crystal layer formed between lower and upper glass substrates.
On the lower glass substrate a plurality of gate and data lines are arranged in a matrix of rows and columns and are spaced apart at a constant interval formed to define a plurality of pixel regions. A switching means in the form of a transistor, for example, a thin film transistor (TFT), is formed at the intersection of the gate and data lines and a pixel electrode is formed in the pixel region.
A black matrix, a color filter layer, and a common electrode are formed on the upper glass substrate. The black matrix prevents leakage of light to the gate lines, data lines, and the TFT region.
Small-sized and lightweight LCD devices for portable televisions, notebook computers, handhelds, personal digital assistants (PDAs) are becoming increasingly popular. Decreasing the weight of such devices is major purpose of technology development. To this end, there are specific efforts to decrease the weight of the LCD itself.
Various methods have been tried to decrease the weight and size of the LCD. However, limitations in the related art and the LCD structure limit the extent to which the weight and size of the main components of the LCD can be reduced.
The glass substrate is one of the most basic elements of the LCD and comprises most of the total weight of the LCD. Accordingly, process technologies are being developed to decrease the total weight of the LCD by decreasing the weight of the glass substrate.
In order to decrease the weight of the glass substrate, its thickness should be decreased preferentially. However, if the thickness decreases below a specific value, the glass substrate is broken during processing and/or cracks are generated. Accordingly, this is one of the limitations in decreasing the thickness of the glass substrate.
A method for decreasing the thickness of the glass substrate currently in wide use is to etch the glass substrate. This etching is performed after an LCD panel has been fabricated by dipping the glass substrate into an etching bath.
This method has disadvantages in that the glass substrate is disproportionately etched. The non-uniform etching is caused by foreign particles generated during the etch process, thereby creating an irregular and/or rough surface on the glass substrate. Additionally, if the substrate becomes uneven, a difference in transmissivity occurs as light passing through the substrate is refracted to an unintended path, thereby creating stains on a liquid crystal screen.
A method for solving the foregoing problems is disclosed in U.S. Pat. No. 6,228,211 B 1, filed by the applicant on Sep. 3, 1999 and claiming priority to Korean Patent Application No. 1998-37000, filed by the applicant on Sep. 8, 1998, both of which are hereby incorporated by reference for all purposes as if fully set forth herein. In the process disclosed in U.S. Pat. No. 6,228,211 B1, impurities generated on the substrate during an etching process are eliminated using an etching apparatus having a bubble plate.
The etching apparatus with the bubble plate will be described in detail with reference to the accompanying drawings below.
FIG. 1 is a simplified sectional view of an etching apparatus of the related art disclosed in U.S. Pat. No. 6,228,211 B1. Referring to FIG. 1, the prior art etching device includes an etching tank 1, a bubble plate 3 formed inside the etching tank 1, and a porous plate 5 formed on the bubble plate 3. An etching solution mixing tank 9 is connected to the bubble plate 3 through an etching solution supply pipe 7. A buffer tank 13 is connected to the bubble plate 3 through the etching solution discharge pipe 11. An air supply pipe 15 is connected to the bubble plate 3 for providing air into the bubble plate.
The etching solution mixing tank 9 is connected to a deionized (DI) water supply part 17, an undiluted etching solution supply part 19, and the buffer tank 13. The etching solution mixing tank 9 can store DI water provided from the DI water supply part 17, the undiluted etching solution (e.g., HF) provided from the undiluted etching solution supply part 19, and purified etching solution provided from the buffer tank 13.
FIG. 2 is a plane view of the bubble plate 3 comprising a rectangular frame 20 and a plurality of air tubes 22 formed inside the rectangular frame 20.
The air tubes 22 have a plurality of holes 26 in their surfaces. The rectangular frame is connected to the air tubes 22 and includes an air path 24 and an air injection hole 28 for providing nitrogen gas and the like from the air supply pipe 15.
A guide 30 is formed on the four corners of the rectangular frame 20 of the bubble plate 3, as shown in FIG. 3. The guide 30 plays a role in fixing the bubble plate 3, a porous plate 5, and a cassette (not shown) on which the substrate is provided. The guide 30 is fixed to the etching tank's inner surface via a bolt.
A method for etching the glass substrate of the LCD panel using the aforementioned related art etching device will be described below.
A glass substrate is placed on a porous plate 5. The etching solution stored in the etching solution mixing tank 9 then passes through the bubble plate 3 via an etching solution supply pipe 7 and is thereby evenly provided on the glass substrate through the holes in the porous plate 5. At this time, nitrogen gas injected into the bubble plate 3 through the air supply pipe 15 passes through the holes of the porous plate 5 forming nitrogen bubbles. These nitrogen bubbles are provided to the glass substrate, thereby eliminating impurities on the surface of the glass substrate.
A filter formed in the etching solution discharge pipe 11 eliminates impurities in the etching solution. The cleaned etching solution is provided to a buffer tank 13 and is subsequently stored in the etching solution mixing tank 9, thereby restarting the circulation.
The aforementioned related art etching apparatus has several problems.
The bubble plate 3 needs to be cleaned and/or replaced regularly as it becomes clogged with sludge generated during the etching process. In order to clean and/or replace the bubble plate 3, it needs to be separated from the etching tank 1. This is done by removing a bolt attaching the guide to the etching tank, after which the etching plate can be removed. After the cleaning and/or replacement, an assembly process should be performed in the opposite order.
The cleaning and/or replacement of the etching plate increases the process time required in the manufacturing of LCD devices. Additionally, workers may be exposed to toxic etchants, such as hydrofluoric acid (HF). Also, defective reassembly may occur, such as the guide being abnormally positioned in the tank, creating etching inferiority and/or substrate damage.